ergonomic seating solutions: recent research and case studies

Ergonomic Seating Solutions: Recent Research and Case Studies

Sharon Joines, PhDDirector of Research

The Ergonomics Center

Karl Marion, MS, CIE, CPESafety & Loss Control Supervisor - Ergonomics

West Virginia Workers' Compensation Commission

Copyright 2003 The Ergonomics Center of North Carolina All Rights reserved.

OverviewOverview

1. Ergonomic seating terminology 2. Guidelines for seating based on a recent review

guidelines, standards, and research3. Considerations when looking for ergonomic

solutions and selecting a chair4. Recent research on pressure distribution5. Case study


Review of GuidelinesReview of Guidelines

Recommendations for seating individuals in an office chair based on a recent review of

- guidelines, - standards, and

- research

Acknowledgements to:Elizabeth Covalla,Hollis Dickens, andJeff Hoyle

Partially funded by:Knape & Vogt


TerminologyTerminology

4

2

3

15

1: Backrest length2: Backrest width3: Distance between arm supports4: Seat pan width5: Arm support width


TerminologyTerminology

11

910

78

66: Seat pan depth7: Arm support length8: Distance between arm support

and seat pan edges9: Backrest angle10: Arm support height11: Seat pan height


Terminology: AnthropometryTerminology: Anthropometry

4

5 PoplitealHeight11: Seat

pan height

Seated Hip Width4: Seat pan

width

Seated Elbow Height10: Arm support height


Seat pan inclination & discomfortSeat pan inclination & discomfort

Finding: Increasing the angle between the trunk and thighs decreases the stress and load placed on the spine.

Implication: Seat pan inclination– Adjustability allows for increased angles between the trunk

and spine. – In combination with the adjustability of backrest

inclination, a positively inclined seat pan moves the spine toward the natural curvature of the spine.

– Chairs with adjustable seat pan inclinations are preferred and cause less discomfort than conventional non-adjustable office chairs.


Backrest inclination & discomfortBackrest inclination & discomfort

Finding: Increasing the angle between the trunk and thighs decreases the stress and load placed on the spine.

Implication: Backrest inclination– Adjustability should allow for increased angles between

the trunk and spine. – Should be pressure adjustable in order to provide

adequate support for different body masses. – Chairs with adjustable backrests are preferred and

cause less discomfort than conventional non-adjustable office chairs.


Lumbar support & discomfortLumbar support & discomfort

Finding: Pain and discomfort are a direct result of inadequate lumbar support, especially in the low back region. Lumbar support needs depend on height, weight, health, and gender.

Implication: Lumbar supports– Traditional fixed height lumbar supports are unlikely to

provide comfortable and appropriate support for the broad range of users.

– Backrest (lumbar support) should accommodate both body weight and size.

– Ideal lumbar support adjustability includes lumbar height, depth, and applied pressure capabilities.


Lumbar support & discomfortLumbar support & discomfort

Implication (cont.): Lumbar supports– Pressure applied to the lumbar region should be

adjustable• Adjustable seat pan – The capability of a seat pan

to slide forward (away from the backrest) and backward (toward the backrest)

• Adjustable backrest depth - The capability of a backrest to slide forward (toward the front of the seat) and backward (away from the front of the seat)

• Inflatable lumbar support within the backrest


Arm supports & discomfortArm supports & discomfort

Finding: Arm support during computer input tasks– reduces upper extremity muscle activity, – decreases perceived exertion, and – improves comfort.

Implication: Adjustable arm supports– meet the needs/preferences of the range of users

and – are more effective in reducing worker discomfort

than fixed arm supports.


Task variabilityTask variability

The postures, ranges of motion, and work intensity are different for various tasks.

Consider:– An employee performing 1 or 2 tasks – An employee performing 5+ tasks – Effect on range of adjustability?


Comparison of Guidelines

Chair Features

BSR

/HFE

S

CSA

BIF

MA

OSH

A

ISO

Res

earc

h

Recommendations Given Current Standards and

Research Goal of Recommendation

Seat Height Adjustable, about the range 14.82 to 21.84 in. (38.0 to 56.0 cm)

To accommodate the range of users to ensure that the thigh-to-torso angle is not less than 90° and the knee joint angle is greater than 90°

Seat Depth Adjustable, about the range 14.82 to 17.94 in. (38.0 to 46.0 cm)

To accommodate upper leg length for the range of users so that the legs can be positioned without compression at the back of the knee and enable the buttocks to be positioned to enable full use of the backrest

Seat Width At least 17.94 in. (46.0 cm) To accommodate hip breadth for the range of users

Seat Pan Angle

Adjustable, about the range 0° to 4° negatively inclined (CSA) and 0° to 25° positively inclined

Minimizes load placed on the trunk resulting in less discomfort and the spine moves toward lumbar lordosis


Guideline Comparisons - continued

Chair Features

BSR

/HFE

S C

SA

BIF

MA

O

SHA

IS

O

Res

earc

h



Seat Cushion

Cushioned and has waterfall front Front edge of seat pan should be rounded

To minimize leg discomfort due to direct seat contact

Movements of the Seat Pan

and Back Support

Independent: see backrest and seat pan angle. Backrest and seat pan should be adjusted to allow for 93° to 120° angle between torso and thighs

Reduces trunk flexion and back load resulting in increased comfort

Lumbar Support Shape

Adequate lumbar support, fit user’s lumbar curve. Provides support to lumbar area

To provide adequate lumbar support for the range of users

Lumbar Support Height

Adjustable, about the range 3.9 to 11.7 in. (10.0 to 30.0 cm)

To provide adequate lumbar support and minimize low back discomfort for the range of users



Chair Features

BSR

/HFE

S C

SA

BIF

MA

O

SHA

IS

O

Res

earc

h



Lumbar Support Depth

Adjustable, optimal ranges not available: needs further research to determine ranges

To accommodate lumbar region for the range of users

Backrest Height

Standard back: 17.55 to 21.45 in. (45.0 to 55.0 cm) from upper surface of seat cushion High back: At least 2.93 in. (7.5 cm) higher than standard back

To provide adequate back support for the range of users

Backrest Width At least 14.04 in. (36.0 cm) To accommodate the back

width for the range of users



Chair Features

BSR

/HFE

S

CSA

BIF

MA

OSH

A

ISO

Res

earc

h



Backrest Angle Adjustable, about the range of

93° to 120°

Minimizes back discomfort and more pressure is transferred to backrest, less on spine

Backrest Lock Lockable at various positions within the backrest adjustment range

Limits the range of motion for user preferences

Chair Tilt Lock Chair lockable at various positions within the tilt range

Limits the range of motion for user preferences

Arm Supports

Supports forearms and does not interfere with movement or tasks, avoid lifting shoulders or leaning to side

Minimizes strain on shoulders and low back during seated office tasks



Chair Features

BSR

/HFE

S

CSA

BIF

MA

OSH

A

ISO

Res

earc

h



Arm Support Height


To accommodate seated elbow height for the range of users performing a variety of tasks

Arm Support Width At least 1.76 in. (4.5 cm) To accommodate forearm

width for the range of users

Arm Support Length

At least 7.02 in. (18.0 cm). Maintain backrest contact

To allow the range of users to sit close to workstation while maintaining contact with backrest

Arm support Setback At least 5.85 in. (15.0 cm) Allows users to sit close to

workstations

Inside Distance between Armrests


Should accommodate for the maximum elbow to elbow breadth of the design population


ConsiderationsConsiderations

1. The individual(s)2. The task (s)

– Other equipment involved in performing tasks

3. The work environment4. Stylistic vs ergonomic

– Seat pan evaluation

5. Training– How the chair supports with their work– Chair features– Ideal posture– Evaluation


Seat pan evaluationSeat pan evaluation

• Participants performed four office tasks for each chair:– upright relaxed

sitting– typing– writing, and – reading tasks


Seat Pan Evaluation Seat Pan Evaluation -- DataData

Seat Type Average Peak Pressure (PSI)

Average Contact Area (in2)

Average Discomfort Rating (0 to 10 scale)

Mfg 1a (BB-J757x - Slab) 4.49 (1.55) A 233.24 (22.84) A 1.80 (1.28) A

Mfg 1b (BB-J757 N1 - Slab) 4.61 (1.39) A 239.13 (21.43) A 2.17 (1.67) A

Mfg 2 5.50 (1.92) B 192.71 (24.49) B 3.60 (2.65) B

Mfg 3 5.90 (1.56) B 207.02 (20.90) C 3.11 (2.21) B

Seat Type Foam Type Seat Pan Width1 (cm)

Material Compression2

(cm) Mfg1a

(BB-J757x - Slab) Slab foam 51.5 4.0

Mfg1b (BB-J757 N1 - Slab) Slab foam 51.5 4.0

Mfg 2 Injection mold polyurethane 46.0 2.0

Mfg 3 Molded urethane 47.0 2.0


Pressure Distribution & Pressure Distribution & Discomfort RatingDiscomfort Rating

C207.02

B192.71

A239.13

A233.24

050

100150200250300

BB-J757

x

BB-J757

N1

Free

dom

Leap

Avg.

Are

a (c

m^2

)

Mfg 1a Mfg 1b Mfg 2 Mfg 3

B3.1

B3.6

A2.2

A1.8

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

BB-J

757 x

BB-J

757 N

1

Free

dom

Leap

Avg

. Dis

com

fort

Mfg 1a Mfg 1b Mfg 2 Mfg 3


Case StudiesCase Studies

Case 1: Small company, fast paced, more money than time• Dimension clarification ‘stature vs. popliteal height’

• Correct measurements• Dynamic workforce• Re-tooling chairs

Case 2: Similar small company, fast paced, employees performing multiple functions, image conscience, more money than awareness

• Style vs. substance


Case StudiesCase Studies

Case 3: Benefits of marketing learned from a large employer in RTP, NC• Tackling ‘presence vs. use’ chair feature issue• Cost: the image of the ergonomics effort

Case 4: Interaction of environment and chair selection mfgrwith clean room environment

• Clean room, slick floors -> poor friction• Awkward posture using stools for clean room• Task: Microscope work

Solution: • chair selection• work station reconfiguration• textured paint on the floor


SummarySummaryThe abundant supply of ergonomic chairs can be overwhelming.

Identify people’s needs while sitting – anthropometry

Identify task requirements

Identify options and features relevant to seating

Review recommendations based on: – Recent review of guidelines, standards, and research

Consider purchasing motivation– Fact based– Financially based– Stylistic or trend based


Thank You

ergonomic seating solutions: recent research and case studies

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